The research continues to concern itself with determining and characterizing those factors which act during mitosis and are responsible for the dissolution of the nuclear envelope membrane, induction of prophasing and reconstruction of the nuclear membrane in the mitotic life of the cell, as studied both in fused cells as well as in single ones. The crucial role of environmental pH and of divalent ions (Ca ions and Mg ions) in these events ultimately led us to concentrate on the important role the mitochondria play in these events. Apparently, the regulation of availability of divalent cation by functioning mitochondria is an important factor in the reformation of the nuclear membrane in mitosis. The use of substances with known effects on mitochondrial function (chloramphenicol and antimycin A) will be utilized in studying further the role of mitochondria in mitosis; as well as the effects of divalent cation chelators, particularly regarding their effect on metaphase to telophase progression. Studies based on electromicroscopy have proven to be crucial and will form an important aspect of the research.